Interpretive Summary: It has been reported that as much as a 70 percent reduction in crop yield can be directly attributed to environmental stress and that only 3.5 percent of the global arable land is unaffected directly or indirectly by sub-optimal growing conditions. Current models of predicted changes in global climate suggest a prolonged period of erratic weather patterns. Large swings in temperature from warm to freezing in winter months are examples of this erratic pattern. These dramatic shifts in temperature often result in an early release in plant dormancy and a significant loss of cold hardiness. This can be disastrous when temperatures later drop well below freezing causing severe injury and death to many crop plants and ornamentals. Despite an exponential increase in our knowledge of freezing tolerance, understanding cold hardiness in a manner that permits one to improve this trait in an economically important crop has proved elusive. This report provides an evaluation of the field of cold hardiness research, documents its complexity, and provides insight into why progress has been lacking. Furthermore, it provides recommendations on how to address plant cold hardiness in a meaningful manner, and outlines critical areas of future research. This information will be used in designing USDA-ARS research goals and will serve as a resource for other scientists working in this field of research.

Technical Abstract: How plants adapt to freezing temperatures and acclimate to survive the formation of ice within their tissues has been a subject of study for botanists and plant scientists since the latter part of the 19th century. In recent years, there has been an explosion of information on this topic and molecular biology has provided new and exciting opportunities to better understand the genes involved in cold adaptation, freezing response, and environmental stress in general. Despite an exponential increase in our understanding of freezing tolerance, understanding cold hardiness in a manner that allows one to actually improve this trait in economically important crops has proved to be an elusive goal. This is partly due to the growing recognition of the complexity of the process of cold adaptation. The ability of plants to adapt to and survive freezing temperatures has many facets, which are often species specific, and are the result of the response to many environmental cues rather than just low temperature. This is perhaps underappreciated in the design of many controlled environment experiments resulting in data that reflects the response to the experimental conditions but may not reflect actual mechanisms of cold hardiness in the field. The information and opinions presented in this report are an attempt to illustrate the many facets of cold hardiness, emphasize the importance of context in conducting cold hardiness research, and pose, in our view, a few of the critical questions that still need to be addressed.